TSKS01 Digital Communication - Lecture 1

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Course Aims 1(2) TSKS01 Digital Communication Lecture 1 Introduction, Repetition of S&S, models After passing the course, the student should be able to reliably perform standard calculations

(questions) be able to briefly account for some common channel models, especially for cables, radio channels and optical channels. (questions) Mikael Olofsson Department of EE (ISY) Div.

1 Course Aims 1(2) TSKS01 Digital Communication Lecture 1 Introduction, Repetition of S&S, models After passing the course, the student should be able to reliably perform standard calculations regarding digital modulation, binary (linear) codes for error control and source coding. (basics) be generally aquainted with modern communication, especially digital communication, i.e. be able to briefly describe several communication techniques. (questions) be able to briefly account for some common channel models, especially for cables, radio channels and optical channels. (questions) Mikael Olofsson Department of EE (ISY) Div. of Communication Systems be able to describe problems that arise in communication situations, using own words, and be able to describe, and in a relevant way, compare methods to counteract those problems. (questions) TSKS01 Digital Communication - Formalia Information & course material: Lecturer & examiner: Mikael Olofsson, mikael@isy.liu.se Problem classes and labs: Mirsad irki!, mirsad@isy.liu.se TVK Chaitanya, tvk@isy.liu.se Examination: Laborations (1hp): Two 4 hour laborations Sign-up on the web Written exam (5hp): 1 simple task Demand: OK 2 questions (5 points each), min 3 4 problems (5 points each), min 6 Pass: 14 points TSKS01 Digital Communication - Lecture 1 2 TSKS01 Digital Communication - Lecture 1 3 Course Aims 2(2) After passing the course, the student should be able to account for the connection between different concepts in the course in a structured way using adequate terminology. (questions) be able to, with some precision, analyze and compare various choices of digital modulation methods and coding methods in terms of error probabilities, minimum distances and related concepts. (problems) be able to implement such communication systems that are treated in the course in block form and empirically evaluate them. (laborations) TSKS01 Digital Communication - Lecture 1 4

2 Languages in Tutorial Sessions A One-way Telecommunication System Packing Error control Digital to analog Medium encoder encoder Modulator coding coding Digital modulation Swedish English Destination decoder decoder Demodulator Unpacking Error correction Analog to digital TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 7 Overview of a Communication Situation Course Contents Transmission channels (Cables, Radio, Optical) (Lectures 1 & 4) Sender Receiver Destination Introduction to stochastic processes. (Lectures 2-3) Software defined radio (lab preparation). (Lecture 5) statistics Stochastic process Markov chains Auto-correlation Sampling Reconstruction D/A-conversion Modulation coding coding Filtering LTI - non LTI Fading Noise Intentional jamming Sampling Reconstruktion A/D-conversion Demodulation -decoding decoding Filtering Demands on quality Cost functions Application Purpose Complex baseband representation. (Lecture 6) Digital modulation. (Lectures 7-9) Codes for error control. (Lectures 10-11) coding (packing data). (Lectures 12) TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 8

3 Repetition Signals and Systems Linear System Signals: Systems: Voltages, currents, and other measurements. Manipulate signals. x(t) System y(t) j 2f t Complex exponential: e 0 = cos(2f t) + j sin(2f t) Unit step: u(t) = 0, t<0 1, t>0 0 0 Unit impulse: Property: (t): x(t)(t) dt = x(0) t u(t) = () d TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 11 Special Outputs Time-Invariant and LTI Impulse response: (t) Energy-free system h(t) Step response: u(t) Energy-free system g(t) General case: x(t) Energy-free system y(t) TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 12

4 Convolution The Frequency domain TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 15 Output of LTI Systems LTI Systems TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 16

5 Cables Two wires: Characteristic Impedance 2(2) We had: Model: Serial properties per meter resistance impedance inductance Possible choice: Result: Z is real and constant Mathematically: Linear differential equation LTI system, impulse response, frequency response admittance capacitance conductance Parallel properties per meter Proper termination: A finite cable should be terminated with the impedance Z TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 19 Characteristic Impedance 1(2) Frequency Response of a Cable 1(2) Model of an infinitely long cable: Solution: Finite length cable: One link: Also infinitely long cable Result: Frequency response of one link: Alternative model: Real part has to be positive: with argument in ( /2,/2) Result: TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 20

6 Frequency Response of a Cable 2(2) The Telephone Approximate amplitude characteristic: Frequency response of a one meter long cable: An a meter long cable: Real-valued characteristic impedance: Due to various filters and modulations in telephone systems TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 23 Limit for the Frequency Response Optical Fibers Sender side Light source Receiver side Light detector LED Laser Photo diode Photo transistor Speed of light in vacuum: c m/s Speed of light in other media: v < c Refraction index: n = c / v Examples: Air: n (1) Fiber glass: 1.5 < n < 1.9 (roughly) TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 24

7 Step-Index Fiber Multmode Graded Index Acceptance half-angle: Acceptance full angle: in = arcsin 2 in Numerical aperture: sin( in ) = ( 2 2 n 1 n 2 ) n 0 n 0 n 1 2 n TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 27 Multimode Propagation Singlemode Step Index Different paths - different distances different delays pulse spreading Light pulse in Light pulse out TSKS01 Digital Communication - Lecture TSKS01 Digital Communication - Lecture 1 28

TSKS01 Digital Communication - Lecture 1

TSKS01 Digital Communication - Lecture 1 Mirsad ýirkiü, mirsad@isy.liu.se TVK Chaitanya, tvk@isy.liu.se Laborations (1hp): Two 4 hour laborations Sign-up on the web Problem classes and labs: Examination: 2012-08-31 Mikael Olofsson, mikael@isy.liu.se